The present invention relates to a key and lock. More particularly this invention concerns such a key and lock designed for particular high-security applications.
In my U.S. Pat. No. 4,977,767 I describe a flat key having a blade formed with a pair of opposite edges, with a pair of opposite faces between the edges, and with an outer-end tip. In addition this blade is formed with bitting along at least one of its edges, with a pair of relatively shallow, outwardly open, and generally parallel but spaced grooves formed in at least one of the faces extending generally longitudinally in a nonstraight path from the tip, and with a relatively deep and outwardly open groove formed in the one face and extending generally longitudinally in a nonstraight path from the tip generally nonparallel to the shallow grooves.
Such a system is extremely effective, but the relatively thin blade of the key is unable to exert considerable torque and is often broken. Furthermore the in-line axial arrangement of the parts of the lock make it susceptible to sophisticated picking.
It is therefore an object of the present invention to provide an improved key.
A further object is to provide an improved lock for the key.
Another object is the provision of such an improved key and lock which are particularly robust and pick-resistant.
A key according to the invention has a blade formed with a part-cylindrical face and with a pair of relatively shallow, outwardly open, and generally parallel but spaced grooves formed in the face extending generally longitudinally in a nonstraight path and a relatively deep and outwardly open groove formed in the face and extending generally longitudinally in a nonstraight path generally nonparallel to the shallow grooves. The grooves each have a plurality of control positions at which they extend substantially parallel to the blade and are inclined to the blade between the respective control positions. The control positions of the shallow grooves are transversely aligned and staggered relative to the control positions of the deep groove.
Thus with this system the key is extremely hard to duplicate. As a result clandestine copying is virtually ruled out. Furthermore the three-dimensional shape of the key face and similar three-dimensional shape of the control grooves allows the key to carry a very complex coding. This can be made even more complex by undercutting the grooves so as to coact with appropriately shaped tumbler formations. The groove walls can be set nonparallel to a diametral plane, so that one wall is in effect undercut.
The key can be solid. It can also be hollow, in which case a nearly-semicylindrical shells can be welded to a tubular core and the grooves can be formed in the shell. This procedure makes it much easier to manufacture a key according to the invention.
In accordance with the invention the deep groove is mainly between the shallow grooves. Furthermore the grooves all flare axially toward a tip of the key.
In another key according to the invention the key blade is cylindrical and has a second part-cylindrical face substantially identical to the first-mentioned part-cylindrical face and formed with second shallow and deep grooves like the first-mentioned shallow and deep grooves. In this case the key is reversible. When a tubular key is employed, it is formed with longitudinal diametrally opposite ridges between which groove-carrying semicylindrical shells are secured. Whether the key is solid or tubular, in this reversible system the key blade is substantially symmetrical to a plane extending between the first and second faces.
To further increase security the blade is formed with at least one axially extending ward formation, normally a groove. In a reversible key, there are two such ward grooves.
For maximum coding possibilities the control positions or each groove are angularly offset from one another. At least three angularly offset positions are possible for each groove, and as many as four, five, or more can easily be provided to maximize security.
The invention further concerns a lock usable with the above-described key and comprising a relatively stationary lock housing, a lock cylinder rotatable in the housing about an axis and formed with an axially outwardly open passage shaped to snugly receive the key blade, a first tumbler angularly displaceable in the cylinder and provided with a first formation engageable generally radially of the axis in the deep groove, and a second tumbler angularly displaceable in the cylinder and provided with a second formation engageable generally radially of the axis in the shallow grooves, whereby the tumblers are shifted angularly on insertion of the key by interengagement of the formations and the respective grooves. A lock element is displaceable in only one predetermined angular position of the tumblers between a position blocking rotation of the cylinder in the housing and a position permitting such rotation.
Normally according to the invention the second tumbler has two such second formations each complementary to a respective one of the shallow grooves and fixedly spaced angularly of the key blade relative to each other. In addition the tumblers are flat annular disks surrounding and defining the passage and lying in planes substantially perpendicular to the axis and the lock is provided with a plurality of such first and second tumblers spaced axially with spacers between the tumblers.